Application ：

package com.example.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.RestController;

@SpringBootApplication
@RestController
public class DemoApplication {
    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
}

json数据bean：

package com.example.demo;

public class JsonData {
    public long id;
    public String data = "";

    public JsonData(long id, String data) {
        this.id = id;
        this.data = data;
    }

    public void setId(long id) {
        this.id = id;
    }

    public long getId() {
        return id;
    }

    public void setData(String data) {
        this.data = data;
    }

    public String getData() {
        return data;
    }
}

控制器controller：

package com.example.demo;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class JsonTestController {
    @GetMapping("/jsontest")
    public JsonData myjsontest(@RequestParam(value = "name", defaultValue = "null") String name) {
        return new JsonData(2021, "zhangphil");
    }
}

注意，路由和函数名一一对应。

启动程序，在浏览器输入： 

http://localhost:8080/jsontest

页面返回内容：

{"id":2021,"data":"zhangphil"}